NASA is backing a mission to study the deep interior of Mars as its next Discovery-class project, following in the footsteps of spacecraft that are already operating at Mercury and the asteroid Vesta. The InSight mission, previously known as the Geophysical Monitoring Station or GEMS, is due for launch in 2016, with a cost cap of $425 million.

InSight won out over two other proposed missions that would have sent probes to the hydrocarbon seas of the Saturnian moon Titan or to the surface of a comet. Today's selection comes amid the wild success of NASA's Curiosity rover on Mars, as well as deep questions about the future of Mars exploration.

In a statement, NASA Administrator Charles Bolden made clear that Mars would be as much of a priority for future exploration as budgets will allow.

"The exploration of Mars is a top priority for NASA, and the selection of InSight ensures we will continue to unlock the mysteries of the Red Planet and lay the groundwork for a future human mission there," Bolden said. "The recent successful landing of the Curiosity rover has galvanized public interest in space exploration, and today's announcement makes clear there are more exciting Mars missions to come."

The future of Mars missionsAfter Curiosity, the only other future Mars probe on NASA's list is the MAVEN orbiter, which is due for launch in late 2013 and will study Mars' upper atmosphere. Citing budgetary concerns, NASA has withdrawn its support from the European-led ExoMars project, which is aimed at sending spacecraft to the Red Planet in 2016 and 2018 to set the stage for the eventual return of Martian samples to Earth.

InSight is actually an acronym of sorts, standing for "Interior Exploration Using Seismic Investigations, Geodesy and Heat Transport." The mission would place a lander on Mars with seismic instruments that could determine whether the Red Planet has a liquid core like Earth's, confirm whether or not Mars has tectonic plates like Earth's, and provide insights into the geological evolution of terrestrial planets such as Mars and Earth.

"InSight will get to the 'core' of the nature of the interior and structure of Mars, well below the observations we've been able to make from orbit or the surface," John Grunsfeld, NASA's associate administrator for science, said in today's statement.

Grunsfeld told reporters that seismological studies have been a standard method for learning about the interior structure of Earth. "We have no such knowledge for Mars," he said. Seismometers were installed on the two Viking landers that were sent to Mars in the mid-1970s, but they sent back little data about Mars' seismicity. (One didn't work, and the other mostly registered wind-induced vibrations because it was placed on one of the lander's legs.)

InSight and the othersJim Green, director of NASA Headquarters' Planetary Science Division, said the InSight mission is slated for launch in March 2016, with landing expected in September 2016. The landing site has not yet been selected, but it will be in a flat, near-equatorial region of the planet, Green said. The mission is due to last one full Martian year, which is nearly two Earth years.

The scientific payload includes a robotic arm, a geodetic instrument to determine Mars' rotation axis and two cameras, plus a French-built seismometer to measure deep seismic waves and a German-built "mole" that can burrow down through several yards (meters) of Martian soil to monitor subsurface heat.

Discovery-class missions are capped at $425 million in 2010 dollars, excluding the cost of the launch vehicle. NASA created the Discovery program to support relatively low-cost planetary missions, as opposed to more costly flagship missions such as the $2.5 billion Curiosity rover. Other Discovery-class missions include the Dawn probe, which is currently at Vesta and will head for the dwarf planet Ceres; Messenger, which is orbiting Mercury; and Stardust, which returned samples from Comet Wild 2. Until now, proposals for Mars missions were excluded from Discovery-class consideration.

NASA received 28 proposals for Discovery-class missions, and narrowed the field to three missions last year. InSight as well as the two others received $3 million each for preliminary design studies. Grunsfeld said InSight was the "most competitive" proposal among the three, which also included:

Titan Mare Explorer (TiME), which would have provided the first direct exploration of an ocean environment beyond Earth by landing in, and floating on, Titan's sea of methane and ethane.

Comet Hopper, which would have studied cometary evolution by landing on a comet multiple times and observing its changes as it interacted with the sun.

Grunsfeld said outside reviewers gave the InSight mission the "highest probability" that it could actually be performed on schedule and on budget. In the current climate of tight budgets, "that was a pretty major distinguishing feature," he said. Green and Grunsfeld said InSight's precise mission cost would be determined next year. Meanwhile, the also-rans could be reconsidered for future opportunities.

The fate of the Mars exploration program is a separate issue, but the fact that InSight was selected as a Discovery-class mission would probably rule out the selection of a similar geophysical station as part of the program's future lineup, Grunsfeld said.

"This is fantastic news for our Mars exploration program, and will answer several key questions about Martian geology and may help us to understand better the processes that led to Mars and the Earth evolving in such different directions, even though there is evidence that abundant water once flowed on the surface of Mars," Schiff said in a statement. "Also, by announcing this new mission soon after the landing of Curiosity, NASA will help to preserve the entry, descent and landing capabilities that were so spectacularly demonstrated by the scientists at JPL, whose talents will be crucial to future planetary exploration."